The attack came a day after Israel briefly closed its airport in the Red Sea resort of Eilat, close to the Sinai, in response to unspecified security warnings. Eilat was previously targeted by rocket fire from the Sinai.

Israel maintained official silence about the strike, suggesting that if the Jewish state was involved, it might be trying to avoid embarrassing the Egyptian military. An Egyptian military spokesman later denied the report but did not provide another cause for the explosion.

Egypt’s official MENA news agency said an explosion destroyed a rocket launcher set up near the border to launch attacks against Israel, and at least five Islamic militants were killed. But it did not elaborate.

An Israeli drone attack in the Sinai could signal a significant new level of security cooperation between the two former foes following a military coup that ousted Egypt’s president, Mohammed Morsi, last month. The military has alleged that Morsi and his Muslim Brotherhood movement had turned a blind eye to Islamic militants in the Sinai.

Meanwhile, Morsi’s ouster, which came after mass protests demanding he step down, has triggered a rise in attacks against security forces on the peninsula, raising fears that extremists could exploit Islamist anger to spread their insurgency.

The Egyptian security officials, who spoke on condition of anonymity because they were not authorized to release the information, said the Israeli attack was launched in cooperation with Egyptian authorities despite past insistence that the government would not allow other countries to use its territories to launch attacks.

Residents heard a large explosion Friday in el-Agra, an area in the northern region of the Sinai close to the border with Israel. The Sinai is also internationally renowned for its Red Sea resorts in the south.

The Israeli military said only that it was looking into the report after being contacted by the AP.

Egyptian military spokesman Col. Ahmed Mohammed Ali initially said on his official Facebook page that security forces were investigating two explosions in el-Agra. He later issued a statement denying “in form and substance any attacks from the Israeli side inside Egyptian territories” and saying the claim of cooperation was “baseless.”

The Egyptian security officials told The Associated Press that the drone had been flying over the site of the attack since early Friday.

Egypt’s military and security forces have long been engaged in a battle against Islamic militants in the northern half of the peninsula. Militants and tribesmen also have been engaged in smuggling and other criminal activity in the area for years.

Amid the political turmoil facing the nation in the more than two years since longtime autocratic leader Hosni Mubarak was ousted, Egypt has adhered to a 1979 peace deal with Israel.

But militants have fired rockets toward Eilat, a major destination for domestic and international tourists on Israel’s southern tip.

Israel briefly closed its airport there on Thursday, citing unspecified security concerns. An Egyptian security official told the AP that officials warned Israel about the possibility of rocket strikes. The official said Egyptian authorities received intelligence suggesting terrorist groups planned to fire missiles Friday at Israel, as well as at locations in northern Sinai and the Suez Canal.